A Paleoproterozoic mantle source modified by subducted sediments under the North China craton. (15th January 2019)

• Record Type: Journal Article
• Authors: Xu, Cheng; Chakhmouradian, Anton R.; Kynický, Jindřich; Li, Yunxiu; Song, Wenlei; Chen, Wei
• Is Part Of: Geochimica et cosmochimica acta. Volume 245(2019)
• Page Start: 222
• Page End: 239
• Publication Date: 2019-01-15
• Subjects: Paleoproterozoic alkaline rocks -- Carbonatites -- Orogenic belt -- Mantle sources -- Subducted sediments -- Modern plate tectonics; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2018.10.032
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Subduction is an effective mechanism for deep recycling of supracrustal rocks and mantle refertilization. However, the timing of the onset of modern-style deep subduction is debated. Here we report geochronogical and geochemical data for an intrusive suite of ultramafic, syenitic and carbonatitic rocks, a carbonatite-hosted peridotite xenolith, and granulites from the Paleoproterozoic Trans-North China orogen in the North China craton (NCC). The xenolith differs in composition from typical cratonic mantle peridotites. It equilibrated at T ≈ 1100 °C and P ≈ 29 kbar, i.e. under hotter conditions than cratonic mantle xenoliths worldwide. The carbonatites and associated alkaline rocks were emplaced at 1810 ± 3 Ma and are related to the Paleoproterozoic collision between the Western and Eastern segments of the NCC. These intrusions show Sr-Nd isotope compositions consistent with an enriched mantle source [( 87 Sr/ 86 Sr)i = 0.7027–0.7039; εNd(t) = −4 to −6], and contain zircon characterized by unradiogenic Hf isotope compositions [εHf(t) = −5 to −9] and high δ 18 Osmow values (7.9–9.5‰). In contrast, basement granulites and wall-rock granites are enriched in radiogenic Nd and Hf isotopes, but low in 18 O. These differences rule out the possibility of crustal contamination. Our results thus suggest that modern-style plate tectonics dates back at least to the Paleoproterozoic Era, and the post-collisional Paleoproterozoic alkaline magmatism in the NCC tapped mantle sources modified by deep sediment recycling.